Low-color stiff pvb laminates for use in aircraft windscreens

ABSTRACT

The present invention describes laminate articles comprising a stiff, low-color PVB resin having a YID of less than 12 and having a low concentration of plasticizer in the resin composition, wherein the resin is prepared from a composition that includes a PVB bleaching compound. The laminate articles of the present invention have high curvature. A laminate of the present invention can be particularly useful for aircraft windscreen applications.

This application claims the benefit of U.S. Provisional Application No.60/363,908, filed Mar. 12, 2002.

BACKGROUND OF THE INVENTION

Plasticized polyvinyl butyral sheet (PVB) is used in the manufacture oflaminate structures such as, for example: windshields for vehiclesincluding automobiles, motorcycles, and boats; homes and buildings;shelving in cabinets and display cases; and other articles wherestructural strength is desirable in a glass sheet. In many applications,it is desirable that the laminate be transparent and colorless, or atleast have very low color. Undesired or unintended color in a glasslaminate can be a result of impurities from various sources. In somecases, color can occur in the PVB interlayer. Color in a PVB sheet canresult from several sources in the PVB resin, or from the manufacturingprocess. For example, color can result from instability of the PVBresin, from impurities, or from other additives present in the PVBcomposition. Color in a PVB sheet can develop during storage of the PVB,or be caused by process conditions to which the resin is subjected.

PVB can be manufactured according to known processes. For example, U.S.Pat. No. 3,153,009 describes a process for commercial manufacture ofPVB. U.S. Pat. No. 4,696,971 also describes a process for manufacturingPVB wherein sodium diocytlsulfosuccinate (DOSS) is used as a surfactant.With some exceptions that will be obvious to one skilled in the art, theteachings of the above-referenced patents are hereby incorporated byreference.

In a conventional PVB sheet manufacturing process, additives aretypically included to protect PVB from developing color. Examples ofsuch additives are antioxidants and light stabilizers. Light stabilizersinclude compounds that are capable of absorbing ultraviolet (UV) lightand/or infrared (IR) light, thereby protecting the resin from theeffects of this radiation. In some commercial applications, it has beenfound that combinations of UV light stabilizers can be required forsatisfactory results. For example, conventional PVB resin compositionscan include, for example, Tinuvin® 123 in addition to Tinuvin® 326 toobtain satisfactory light stability in the resin. However, usingcombinations of light stabilizers can add additional expense andcomplexity to the manufacturing process.

Conventional PVB resin sheet compositions can also require antioxidantsto prevent oxidation of components in the PVB that are subject tooxidation, and can contribute to the color of the resin in an theoxidized state. For example, octylphenol can be used in combination withlight stabilizers to give a PVB sheet with acceptable color and colorstability. However, the effectiveness of antioxidants and lightstabilizers can be dependent upon the composition of the PVBcomposition. Changing the PVB composition can make the antioxidant andlight stabilizer ineffective in preventing the formation ofcolor-bodies.

Conventional PVB sheet typically includes a plasticizer in order toincrease the flexibility and processibility of the PVB resin. Generally,the higher the concentration of plasticizer, the more flexible thesheet. Various plasticizers are conventional in the manufacture of PVB,and include such plasticizers as: diesters of polyethylene glycols suchas triethylene glycol di(2-ethylhexanoate) (3GO) and tetraethyleneglycol diheptanoate (4G7), for example. Typically, plasticizer isincluded in amounts of greater than 30 pph, based on the total weight ofthe resin. Depending upon the application, as well as other factors,highly plasticized PVB typically can have as much as 60 pph ofplasticizer.

In some special applications, however, it can be desirable to includesmall amounts of plasticizer so that a stiff PVB resin sheet can beobtained. One problem with using low plasticizer concentrations is thatthe PVB composition may require exposure to higher temperatures in orderto extrude the resin and/or to shape the extruded resin sheet for use inthe application for which it was intended. However, when a conventionalPVB resin is exposed to such high temperature, color can develop in theresin thereby making it unusable in applications where clarity and highlaminate transparency are critical.

It can be desirable in the art of manufacturing PVB sheet, to have aprocess for making a low color PVB resin having a low concentration ofplasticizer whereby the PVB composition would not develop a high colorlevel upon exposure to high process temperatures.

It can also be desirable to have a process whereby the color of a PVBresin can be improved by proper selection of additives used in a processfor manufacturing PVB.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a small laminate articlehaving high curvature comprising a plasticized PVB resin interlayerwherein the PVB resin consists essentially of: polyvinylbutyral having ahydroxyl number of from about 15 to about 25; a plasticizer orplasticizer mixture present in a finite amount of less than about 30 pphbased on the dry weight of the resin composition; a surfactant; andoptionally including either (i) a PVB bleaching compound, or (ii) anantioxidant, or (iii) both (i) and (ii), wherein the interlayer wasobtained after extrusion at a temperature in the range of from about225° C. to about 245° C., and wherein the interlayer has a yellownessindex (YID) color of less than about 12.

In another embodiment, the present invention is an aircraft windscreencomprising a plasticized PVB resin interlayer wherein the PVB resinconsists essentially of: polyvinylbutyral having a hydroxyl number offrom about 15 to about 25; a plasticizer or plasticizer mixture presentin a finite amount of less than about 30 pph based on the dry weight ofthe resin composition; a surfactant; and optionally including either (i)a PVB bleaching compound, or (ii) an antioxidant, or (iii) both (i) and(ii), wherein the interlayer was obtained after extrusion at atemperature in the range of from about 225° C. to about 245° C., andwherein the interlayer has a yellowness index (YID) color of less thanabout 12.

DETAILED DESCRIPTION

In one embodiment, the present invention is small laminate articlehaving high curvature comprising a plasticized PVB resin interlayerwherein the PVB resin consists essentially of: polyvinylbutyral having ahydroxyl number of from about 15 to about 25; a plasticizer orplasticizer mixture present in a finite amount of less than about 30 pphbased on the dry weight of the resin composition; a surfactant; andoptionally including either (i) a PVB bleaching compound, or (ii) anantioxidant, or (iii) both (i) and (ii), wherein the interlayer wasobtained after extrusion at a temperature in the range of from about225° C. to about 245° C., and wherein the interlayer has a yellownessindex (YID) color of less than about 12.

PVB can be manufactured according to known processes. For example, U.S.Pat. No. 3,153,009 describes a process for commercial manufacture ofPVB. U.S. Pat. No. 4,696,971 also describes a process for manufacturingPVB wherein sodium dioctylsulfosuccinate (DOSS) is used as a surfactant.With some exceptions that will be obvious to one skilled in the art, theteachings of the above-referenced patents are hereby incorporated byreference.

The PVB resin composition of the present invention includes theplasticizer in a finite amount, but at a concentration of less than 30pph, based on the dry weight of the PVB resin composition. The presentinvention preferably includes plasticizer in an amount of from about 5to about 30 pph, more preferably the plasticizer content is from about15 to about 30 pph. Even more preferably the plasticizer content is fromabout 18 to about 28 pph, and most preferably from about 18 to about 22pph.

The term flake, as used in the present invention, describes a particularphysical form of PVB resin material, that is, granular or particulateversus a film or a sheet. The physical form of the resin does notnecessarily indicate a different PVB composition within the presentapplication, even though sheets and/or films may include additives notfound in the resin flake.

Plasticizers of the present invention can be chosen from any that areknown or used conventionally in the manufacture of plasticized PVBsheeting compositions. For example, a plasticizer suitable for useherein can be a plasticizer or a mixture of plasticizers selected fromthe group consisting of: diesters obtained from the chemical reaction ofaliphatic diols with carboxylic acids, including diesters of polyetherdiols or polyether polyols; and, esters obtained from polyvalentcarboxylic acids and aliphatic alcohols. For convenience, whendescribing the sheet compositions of the present invention, a mixture ofplasticizers can be referred to herein as “plasticizer”. That is, thesingular form of the word “plasticizer” as used herein can represent theuse of either one plasticizer or the use of a mixture of two or moreplasticizers in a given sheet composition. The intended use will beapparent to a reader skilled in the art. Preferred plasticizers for useherein are diesters obtained by the reaction of triethylene glycol ortetraethylene glycol with aliphatic carboxylic acids having from 6 to 10carbon atoms; and diesters obtained from the reaction of sebacic acidwith aliphatic alcohols having from 1 to 18 carbon atoms. Morepreferably the plasticizer is either 4G7, 3GO or dibutyl sebacate (DBS).Most preferably the plasticizer is 3GO.

The composition of the present invention optionally includes at leastone PVB bleaching compound. A PVB bleaching compound (bleachingcompound) of the present invention is any compound that can reduce oreliminate color from a PVB sheet relative to the color of an otherwiseidentical composition, treated using an identical or similar process,with the exception that a bleaching compound is not present. The mode ofthe bleaching action demonstrated by the bleaching compound is notcritical to the present invention. For example, a bleaching compounduseful in the practice of the present invention can be a compound thatreacts directly with color-forming compounds (color bodies) present in aPVB sheet composition, or a compound that is capable of yielding acompound that reacts directly with color-bodies. A bleaching compoundcan be a compound that can decompose in situ to yield decompositionproducts capable of reacting with color bodies present in a PVB sheetcomposition. A bleaching compound in the practice of the presentinvention can be a compound that inhibits the formation of color bodies.Bleaching compounds of the present invention include, for example,inorganic bisulfites such as sodium or potassium bisulfite; organicbisulfites such as tetramethylammonium bisulfite; and compounds similarin structure or function. Bleaching compounds also includesulfosuccinates such as dialkyl sulfosuccinates. For example, thepresent invention can include DOSS as a bleaching compound.

A bleaching compound of the present invention can be included in anyeffective finite amount. An effective amount for the purposes of thepresent invention is any amount that reduces the color of a PVB sheetrelative to the color of an identical or substantially similar PVB sheetcomposition without the bleaching compound. Color measurement can bedone according to any conventional standard practice. Alternatively, inthe absence of comparative data, an effective amount is any amount thatreduces the color of a PVB sheet to a yellowness index (YID) of lessthan about 12 YID. Preferably the YID is less than about 10, morepreferably less than about 8, and most preferably less than about 6.

A bleaching compound can be included in an amount of from about 0.01 toabout 0.85 pph, based on the weight of polyvinyl alcohol (PVA) used inthe preparation of PVB. Preferably, the bleaching compound is present inan amount of from about 0.05 to about 0.80 pph, more preferably in anamount of from about 0.10 to about 0.75 pph, and most preferably in anamount of from about 0.15 to about 0.70 pph. While color reduction in aPVB sheet is an important consideration, the amount of bleachingcompound included will also be a function of the cost of production andthe other properties that may be affected by including the additive.

The present invention includes a surfactant. A surfactant suitable foruse herein can be any that is known to be useful in the art ofpolyvinylbutyral manufacture. For example, surfactants suitable for useherein include: sodium lauryl sulfate; ammonium lauryl sulfate; sodiumdioctyl sulfosuccinate; ammonium perfluorocarboxylates having from 6 to12 carbon atoms; sodium aryl sulfonates, adducts of chlorinatedcyclopentadiene and maleic anhydride; partially neutralizedpolymethacrylic acid; alkylaryl sulfonates; sodium N-oleyl-N-methyltaurate; sodium alkylaryl polyether sulfonates; triethanolamine laurylsulfate; diethyl dicyclohexyl ammonium lauryl sulfate; sodiumsecondary-alkyl sulfates; sulfated fatty acid esters; sulfated arylalcohols; and the like. Preferable surfactants include sodium laurylsulfate, sodium dioctyl sulfocuccinate, sodium cocomethyl tauride, anddecyl(sulfophenoxy)bezenesulfonic acid disodium salt.

The surfactant can be included in any effective amount for theparticular set of process conditions practiced. The surfactant can beincluded in an amount of from about 0.01 to about 0.85 pph by weight,based on the weight of PVA used to prepare PVB. Preferably thesurfactant is included in an amount of from about 0.10 to about 0.80pph. More preferably, the surfactant is included in an amount of fromabout 0.15 to about 0.75 pph. Most preferably, the surfactant isincluded in an amount of from about 0.15 to about 0.70 pph.

The surfactant and the bleaching compound can be the same compound, orcan perform both functions. The bleaching compound is optional only inthe event that the surfactant can also perform the function of ableaching compound. Otherwise the bleaching compound is considered to beessential in the practice of the present invention. For example, DOSScan be used in the practice of the present invention as a surfactant.DOSS can also be a bleaching compound in the practice of the presentinvention. In one particularly preferred embodiment, DOSS can beincluded as both a surfactant and as a bleaching compound. In thisembodiment, the use of a bleaching compound other than DOSS is optional.

Antioxidants can be optionally included in a PVB composition of thepresent invention during sheet preparation to inhibit the oxidation ofthe PVB sheet and/or components. Preferred antioxidants are knownconventionally and available commercially. Most preferred arebis-phenolic antioxidants, which are surprisingly more suitable forpreparing low color PVB sheeting, particularly when 3GO is used asplasticizer. Bis-phenolic antioxidants are available and can be obtainedcommercially. Suitable bis-phenolic antioxidants include2,2′-ethylidenebis(4,6-di-t-butylphenol);4,4′-butylidenebis(2-t-butyl-5-methylphenol);2,2′-isobutylidenebis(4,6-dimethylphenol); and2,2′-methylenebis(6-t-butyl-4-methylphenol), for example. Bis-phenolicanti-oxidants are commercially available under the tradename of ANOX™29, LOWINOX® 22M46, LOWINOX® 44B25, and LOWINOX® 221B46, for example.

An antioxidant can be included in any effective finite amount.Preferably, the antioxidant is included in an amount of from about 0.01to about 0.6%, based on the total weight of the sheet. More preferably,the antioxidant is present in amount of from about 0.03 to about 0.3%,most preferably in an amount of from about 0.05 to about 0.25%.

Other additives are known conventionally to be useful, and can beincluded in a sheet composition of the present invention. Such additivesinclude: light stabilizers, particularly UV light stabilizers, such asTinuvin® P; Tinuvin® 326, and Tinuvin® 123. UV light stabilizers canstabilize the PVB composition by absorbing ultraviolet light andpreventing unwanted effects by the UV light on the PVB. Adhesion controlagents such as alkali and alkaline earth metal salts of carboxylicacids, alkaline earth metal salts of inorganic acids, or a combinationof such salts can be added. Surface tension controlling agents such asTrans® 290 or Trans® 296 available from Trans-Chemco; or Q-23183A®available from Dow Chemical can be used in the practice of the presentinvention. The use Trans® 290 or Trans® 296 is preferred.

A PVB resin of the present invention can be obtained by processes knownin the art of PVB manufacture. PVB resins used in the practice of thepresent invention can be prepared by mixing PVA with butyraldehyde in anaqueous medium in the presence of an acid or mixture of acids, at atemperature of from 5° C. to 100° C.

Typically, the ratio of PVA to butyraldehyde can be chosen such that thePVB has residual hydroxyl functionality, conventionally reported as OHnumber. Residual hydroxyl functionality can vary according to whatproperties are desirable in the PVB. The relative amounts ofbutyraldehyde and PVA required to obtain the desired OH number in thePVB resin will be readily apparent to those skilled in the art of PVBmanufacture. In the practice of the present invention residual hydroxylcan be in the range of from about 14 to about 30. Preferably, the OHnumber is from about 15 to about 25. More preferably, the OH number isfrom about 15 to about 20, and most preferred in the practice of thepresent invention is PVB resin having an OH number in the range of fromabout 17 to about 19. The OH number can be determined according tostandard methods such as ASTM D1396-92.

In a preferred embodiment, a low color PVB sheet of the presentinvention can be obtained by a process comprising the steps: (I)admixing polyvinyl alcohol, butyraldehyde, an acid or mixture of acids,water, and a surfactant (II) stabilizing the mixture obtained in step(I) by (a) raising the pH of the mixture to at least pH 10 (b) isolatingthe resin by draining the liquid, (c) washing the resin with neutral pHwater; (III) plasticizing the PVB resin composition with from about 10to about 30 pph of plasticizer based on the dry weight of the PVB resin;(IV) optionally mixing (a) a PVB bleaching compound and/or (b) anantioxidant and a UV light stabilizer with the PVB resin composition;and (V) extruding the PVB sheet composition at a temperature of fromabout 225° C. to about 245° C. to obtain a PVB sheet having a T_(g) inthe range of from about 35° C. to about 60° C., and a YID of less thanabout 12.

The steps of the process described herein can be carried out in variedorder. For example, while it can be necessary to carry out step (I)before step (II) it is not essential, for the purpose of obtaining a lowcolor sheet of the present invention, that steps (III) or (IV) becarried out in any particular order. Although it may be preferable toimplement these steps just prior to, or simultaneous with, step (V).Also, the order of addition of components is not critical in thepractice of the present invention, although a skilled artisan willrecognize that there may be other benefits of carrying out the processin a consistent and ordered manner. For example, plasticizer can bemixed with the PVB either before or during the extrusion of the PVBcomposition, as described in U.S. Pat. No. 5,886,075.

Plasticizer can be added in any amount desirable to obtain a plasticizedPVB composition. To obtain a stiff PVB sheet in one embodiment of thepresent invention, plasticizer is added in an amount of less than about30 pph, based upon the total dry weight of the resin. The “dry weight”as used herein refers to the weight of the resin after water has beenremoved from the resin.

The glass transition temperature (Tg) of a PVB sheet is dependent inpart upon the concentration of plasticizer included in the composition.A PVB sheet useful in the practice of the present invention has a Tg offrom about 35° C. to about 60° C., as measured by Dynamic MechanicalAnalysis ASTM D4065 (DMA), using the tangent delta (phase shift at 1 Hz)data as indicator. Preferably, the Tg is from about 40° C. to about 57°C., more preferably from about 45° C. to about 57° C., most preferablyfrom about 50° C. to about 55° C.

In one of the preferred embodiments of the present invention, a stiffPVB sheet can be obtained having low color and low concentration ofplasticizer. For sheet having low concentration of plasticizer, it canbe necessary to extrude the sheet at a higher temperature than whenusing higher amounts of plasticizer. For example, PVB resin plasticizedwith from about 5 to about 30 pph plasticizer can be extruded at atemperature of from about 225° C. to about 245° C. Preferably the resincan be extruded at a temperature of from about 227° C. to about 245° C.More preferably, the resin can be extruded at a temperature of fromabout 228° C. to about 242° C., and most preferably from about 230° C.to about 240° C.

A low color PVB sheet suitable for the purposes herein can be obtainedby a process that comprises the steps of: (1) isolating PVB flake from aPVA/butyraldehyde reaction mixture previously described herein; (2)optionally admixing an antioxidant and a UV light stabilizer with theplasticizer to obtain a plasticizer/additive mixture (plasticizermixture); and (3) co-extruding the flake, plasticizer, antioxidant, andUV light stabilizer, or alternatively co-extruding the flake and theplasticizer mixture at a feed ratio of plasticizer mixture to dry offlake from about 5:100 (wt:wt) to about 30:100 (wt:wt) at a temperatureof from about 225° C. to about 245° C. to obtain a low-color PVB sheethaving a YID of less than about 12. It is preferable to admix theantioxidant/UV light stabilizer with the plasticizer prior to extrusionof the sheet.

Laminates of the present invention can be useful as specialty glasslaminates, such as on aircraft. Toughness, transparency and clarity areimportant considerations in applications such as these. Just asimportant is the protection afforded by the interlayer againstsplintering and expulsion of glass particles in the event of accidentalor intentional impact against the glass laminate.

A laminate of the present invention can be obtained by a processcomprising the steps of: putting together at least one layer of curvedspecialty glass with at least one layer of PVB of the present inventionto make a glass/PVB assembly; placing the assembly into a bag capable ofsustaining a vacuum; drawing air out of the bag using a vacuum line orother means of pulling a vacuum on the bag; sealing the bag whilemaintaining the vacuum; placing the sealed bag in an autoclave at atemperature of from about 130° C. to about 180°, at a pressure of fromabout 200 psi (15 Bars), for from about 10 to about 50 minutes.Preferably the bag is autoclaved at a temperature of from about 140° C.to about 160° C. for 20 minutes to about 45 minutes, more preferably ata temperature of from about 145 to about 160° C. for about 20 to 40minutes, and most preferably at about 145° C. to about 155° C. for about25 to about 35 minutes.

The aircraft glass prior to lamination can have functionality embeddedin the glass or on the surface of the glass. For example the glass canhave various antennae or sensors embedded in the glass or on the surfaceof the glass. Such specialty glass is known or can be obtainedcommercially. In any event, the presence of said functionality does notadd to nor detract from the novelty of the presently claimed invention.

The aircraft glass of suitable for use herein can have a high curvature.Lamination of the PVB of the present invention to glass having highcurvature can require lamination conditions described herein. The curvedglass can have a curvature of from about 0.1 miliradian to about 3.2radians with a radius of curvature of from about 20 cm to about 350 cm.

Laminates of the present invention can include an additive to block thetransmission of UV light through the laminate. The additive ispreferably the same additive as the UV light stabilizer. UV light ispreferably absorbed by the laminate so that less than 10% of UV light istransmitted through the laminate. Preferably less than 8% of the UVlight is transmitted through the laminate, more preferably less than 6%UV light is transmitted, and most preferably less than 3%.

PVB interlayers of the present invention have a thickness of greaterthan 0.254 mm. Preferably, PVB interlayers of the present invention havea thickness in the range of form about 0.254 mm to about 1.6 mm.Multiple layers of PVB can be laminated together or in alternate layersof a laminate. Such multilayer laminates can have PVB interlayers thathave a total thickness of greater than 1 mm. Where it is desirable toobtain a laminate wherein the total interlayer thickness is at least 1mm thick, the YID of the interlayer should not be greater than 12,because the transparency of the laminate can be substantially reduced.

EXAMPLES

The following Examples and comparative examples are presented to furtherillustrate the present invention. The Examples are not intended to limitthe scope of the invention in any manner, nor should they be used todefine the claims or specification in any manner that is inconsistentwith the invention as claimed and/or as described herein.

Analytical tests for Hydroxyl number and YID were performed for each ofthe examples and comparative examples according to the methods below.

Hydroxyl number: ASTM D 1396-92.

Sheet Yellowness Index (YID)

A PVB chip is made with 21.0 grams of sheet, and heat pressed into a10.0 mm thick disk of 50.8 mm diameter. Chip preparation involvespreheating a stack of 50.8 mm disks cut from the sheet in a mold for oneminute at 2200 N force and 185° C., then increasing the pressing forceto 32,000 N at 185° C. for two minutes, and cooling under the same forcefor 7.5 minutes. No residual surface pattern that was on the extrudedsheet is visible in the chip. Yellowness index was determined per ASTMD1925-70 on the 10.0 mm thick chip.

Glass Transition Temperature—T_(g) is determined by DMA using theprocedure of ASTM D4065, using the tangent delta at 1 Hz.

Example 1

Poly(vinyl butyral) sheet was prepared as follows: at 90° C., a mixturecomprising 32 parts by weight of poly(vinyl alcohol) of average degreeof polymerization 618 and 99.5% hydrolyzed and 68 parts by weight of PVAof average degree of polymerization 1005 and 99.5% hydrolyzed wasdissolved in 615 parts by weight of demineralized water. To thissolution was added 1 part by weight of 88% para-toluene sulfonic acidand enough sulfuric acid to bring the dissolved PVA solution to a pH of2. Using the procedure described in U.S. Pat. No. 3,153,009, 62 parts byweight of n-butyraldehyde and 0.47 parts by weight of 70% DOSS and thePVA solution were charged into a vessel maintained at 90° C. After a onehour hold time, a slurry was obtained and the slurry was stabilized witha sodium hydroxide solution to raise the pH to 11. Concurrent with thestabilization, 0.07 parts by weight Trans® 290 surface tensionstabilizing agent was added. The slurry was then washed and cooled withdemineralized water. A granular, white PVB resin with residual hydroxylnumber of 18.6 was obtained. The flake was mixed with 3GO plasticizercontaining 4 grams per liter of Tinuvin® P and 8 grams per liter ofLowinox® 44B25 antioxidant and was extruded so that the residence timein the extrusion system was about 15 to 25 minutes. The feed rate ratioof plasticizer to dry flake was 35:100 (wt:wt). Potassium formatesolution was injected so as to deliver a potassium concentration of 10parts per million (ppm) in the sheet. Melt temperature measured at theslot die was between 210 and 215° C. Sheet. YID was 5.85.

Example 2

PVB sheet was made in the manner as in Example 1, except that the feedratio of the plasticizer to dry PVB flake was 20:100, and the meltresidence time was 25 to 40 minutes. Melt temperature at the die was233° C. Sheet yellowness index was 5.05.

Example 3

PVB sheeting was made in the same manner as in Example 2, except thatthe surface pattern due to melt fracture was quenched in a water bath asdisclosed in U.S. Pat. No. 5,886,075 by Keene et al. Melt temperaturewas between 225° C. and 230° C. Sheeting YID was 4.80, andwashboard-shape pattern was clearly visible on the surface of thesheeting.

Comparative Example C1

PVB flake was prepared as in Example 1 except that 0.4 parts by weightof sodium lauryl sulfate, based on PVA, was used in the place of dioctylsodium sulfosuccinate as the surfactant in the PVB preparation step, andno other surface tension modifiers were added. A granular, white PVBresin with residual hydroxyl number of 18.6 was obtained. Using theflake made with sodium lauryl sulfate as described here, sheet wasprepared as in Example 1, except that the feed ratio of plasticizer todry flake was 35:100. Melt temperature measured at the slot die wasbetween 210 and 213° C. Sheet yellowness was 25.05.

Comparative Example C2

The flake described in Example C1 was used to prepare sheet as inExample 1, except that the feed rate ratio of 3GO plasticizer to dryresin of 24:100, and the potassium level in the sheet was 50 ppm, andthe melt residence time in the system was 25-40 minutes. Melttemperature at the die was between 228 and 233° C. Sheet yellowness was53.82.

1. A small laminate article having high curvature comprising a plasticized PVB resin interlayer wherein the PVB resin consists essentially of: polyvinylbutyral having a hydroxyl number of from about 15 to about 25; a plasticizer or plasticizer mixture present in a finite amount of less than about 30 pph based on the dry weight of the resin composition; a surfactant; and optionally including either (i) a PVB bleaching compound, or (ii) an antioxidant, or (iii) both (i) and (ii), wherein the interlayer was obtained after extrusion at a temperature in the range of from about 225° C. to about 245° C., and wherein the interlayer has a yellowness index (YID) color of less than about
 12. 2. The article of claim 1 wherein the surfactant is DOSS.
 3. The article of claim 1 wherein the PVB resin includes a bleaching compound.
 4. The article of claim 3 wherein the bleaching compound is DOSS.
 5. The article of claim 4 wherein the article is a laminate comprising at least one layer of PVB and at least one layer of glass wherein the PVB layer has a thickness in the range of from about 0.254 mm to about 1.6 mm.
 6. The article of claim 5 wherein the laminate comprises more than one PVB interlayer, and wherein the combined thickness of the PVB interlayers is in the range of from about 0.75 to about 1.6 mm.
 7. The article of claim 5 wherein the laminate is useful as aircraft glass.
 8. The article of claim 5 wherein the laminate is obtained by a process comprising the steps of: (i) putting together at least one layer of curved specialty glass with at least one layer of PVB of the present invention to make a glass/PVB assembly; (ii) placing the assembly into a bag capable of sustaining a vacuum; (iii) drawing air out of the bag using a vacuum line or other means of pulling a vacuum on the bag; (iv) sealing the bag while maintaining the vacuum; (v) placing the sealed bag in an autoclave at a temperature of from about 130° C. to about 180°, at a pressure of from about 200 psi (15 Bars), for from about 10 to about 50 minutes. 